Plexiform melanocytic schwannoma: a mimic of melanoma.

We present a unique dermal tumor for which we propose the term plexiform melanocytic schwanomma. The proliferation consisted of lobules of epithelioid and spindled cells with S100, Melan-A and HMB-45 positivity but without obvious melanin pigmentation. The nuclei were moderately pleomorphic in some areas, and in a few areas the mitotic index was elevated. Schwannian differentiation was inferred from the presence of areas with nuclear palisading resembling Verocay bodies, from plexiform architecture and from the presence of a thin rim of EMA positivity around the tumor. Array-based comparative genomic hybridization showed genomic losses that overlap with those seen in sporadic schwanomma. The differential diagnosis included melanoma, melanotic schwannoma and cutaneous melanocytoneuroma, and we compare and contrast our case with these entities.